In-flight refueling (or air-to-air refueling) is an important method for extending the range of aircraft traveling long distances over areas having no feasible landing or refueling points. Although in-flight refueling is a relatively common operation, especially for military aircraft, the aircraft to be refueled (e.g., the receiver aircraft) must be precisely positioned relative to the tanker aircraft in order to provide a safe engagement while the fuel is dispensed to the receiver aircraft. The requirement for precise relative spatial positioning of the two rapidly moving aircraft makes in-flight refueling a challenging operation.
The are currently two primary systems for in-flight refueling. One is a probe and drogue system in which a refueling hose having a drogue disposed at one end is trailed behind the tanker aircraft and is engaged by the receiver aircraft. Another system is a boom refueling system. The boom refueling system typically includes a rigid boom extending from the tanker aircraft, with a nozzle at its distal end. The boom also includes airfoils controlled by a boom operator stationed on the refueling aircraft. The airfoils allow the operator to maneuver the boom with respect to the receiver aircraft. Accordingly, the receiver aircraft is first maneuvered into an in-flight refueling position below and aft of the tanker aircraft. The boom operator then controls the airfoils to position the boom and mate the refueling nozzle with a refueling connection on the receiver aircraft.
In order to accommodate the inevitable relative motion between the tanker aircraft and the receiver aircraft, the refueling boom must be movable, both vertically and laterally. Accordingly, the refueling boom and associated supply lines (e.g., electrical supply lines and hydraulic lines) must be configured to accommodate this relative motion. In particular, hydraulic fluid is typically used to move the boom airfoil surfaces, and accordingly must be provided to the boom from the fixed reference point of the aircraft to the moving boom. One existing method for accommodating this relative movement is to provide a relatively large degree of “slack” in the hydraulic lines, which allows them to flex and bend as the boom moves relative to the aircraft. One potential drawback with the foregoing approach is that the volume required by the boom as a result of the increased volume occupied by the lengthy hydraulic lines is increased. Because the boom is positioned external to the aircraft, the increased volume can increase the drag of the aircraft. The increased drag increases the cost of flying the aircraft. Furthermore, the lengthy hoses can become cumbersome during operations.